text:
How common is it in current British usage for the angle between the chord line of a wing and the flight path to be called the "angle of incidence"?
In American usage, the angle between the chord line of a wing and the flight path is called the "angle of attack".  The angle of attack is also represented by the greek letter "alpha".  However, some British authors, especially in the past, have referred to this angle as the "angle of incidence".  (See one supporting reference here.)
We'll call this the "older British" use of the term "angle of incidence".  How common is this usage now in the British aviation world?  Has it completely fallen by the wayside, or is still common?  Was it ever very common?
Also, what term or terms did authors and speakers following this "older British" usage, use to refer to the angle between the wing chord and the longitudinal axis of the fuselage (or some other similar defined datum line approximating the longitudinal axis of the fuselage?)  Some of the terms that have been used for this angle by writers and speakers following the "older British" usage noted above, appear to include "rigger's angle" and "rigger's angle of incidence".  Are there others?
(In American usage, this latter angle is in fact the angle that is called the "angle of incidence".)
(Bonus extra part: is there one particular greek letter that is normally assigned to this latter angle in engineering texts and papers, much as "alpha" is normally assigned to the angle that is described in the first paragraph of this question?)

Apparently the French have yet another system of terminology, but I'll save that for another question.

This article would benefit from an original-source example of the "older British" usage of "angle of incidence" but I have none handy at the time.  I definitely have seen references to this practice elsewhere than in the link cited above.

On your link it is the chord line not the longitudinal axis

You says yesterday that in american angle of attack is the angle between the chord and the relative wind.not the path

Oh sorry :RELATIVE WIND is the relative movement of air relative to the plane;
it is ALWAYS PARALLEL AND SENSE OPPOSITE to the TRAJECTORY OF THE AIRPLANE.http://www.volez.net/aerodynamique-technique/elements-aerodynamique/resistance-air-vent-relatif.html

From A.C. Kermode; Mechanics of Flight, London, Pitman, 8th Edn, 1972, p.75 (his bold):

"We call the angle between the chord of the aerofoil and the direction of the airflow the angle of attack.
"This angle is often known as the angle of incidence; the term was avoided in early editions of this book because it was apt to be confused with the riggers' angle of incidence, i.e. the angle between the chord of the aerofoil and some fixed datum line in the aeroplane. Now that aircraft are no longer "rigged" (in the old sense) there is no objection to the term angle of incidence; but by the same token there is no objection either to angle of attack, many pilots and others have become accustomed to it; it is almost universally used in America, and so we shall continue to use it in this edition."

And from L.J. Clancy; Aerodynamics, London, Pitman, 1975, p.56:

"The attitude of the aerofoil, as expressed by the angle between the chord line and the free stream velocity vector ... , denoted by $\alpha$, is called the incidence, or angle of attack."

In contrast to Kermode, Clancy goes on to use "incidence" throughout. Note that this contrast appears in technical books from the same publisher, just three years apart. It was, and is, no big deal.
In my experience, anybody with the slightest technical interest in flight is familiar with both usages and they both still get used interchangeably in the UK.
I have not seen a standard symbol for the rigging angle, presumably because it is of irrelevance to the aerodynamicist. It was once, and occasionally still is, alternatively referred to by its French name of décalage.

Thanks for added note in the last sentence, you can see that if a French person speaking English refers to the rigging angle as the "decalage" and the angle-of-attack as the "angle of incidence" there is opportunity for tremendous confusion in a conversation with an English-speaking person especially one unfamiliar with the older/less common usage of the term.  Now add in one more twist for more potential confusion--

Now add in one more twist for more potential confusion-- a French person has recently informed me that a French term translating directly to "angle-of-attack" is used specifically to refer to the angle between the fuselage and the airflow.  Stay tuned for another question seeking to verify whether this is really true in widespread usage.  Was discussed here-- https://chat.stackexchange.com/rooms/106037/a-room-to-talk-about-american-british-and-french-usage-of-angle-of-attack-a

I have never met anybody with whom a quick "by incidence do you mean angle of attack or rigging angle?" has not avoided the enormity you refer to. Vast numbers of English words have inherent ambiguity and one must take a pragmatic view of these things or one is doomed. It soon comes with experience, let the tyro beware.

Yes it was just the perfect storm of two people with two different native languages using different and conflicting definitions for three different terms simultaneously without at first understanding what was going on.  The "incidence" thing alone is easily resolved.


text:
A question about the exact meaning of one British usage of the term "Angle of Incidence"
This answer to a related question stated:

Most anything can have an angle of attack. If you must be specific,
  you mention 'angle of attack of ...'

...

When we talk about airplane as a whole, usually the 'default' angle of
  attack is the one between the wind and the body frame (in the vertical
  plane). How body frame is defined depends on the aircraft designer,
  but normally X goes along the fuselage. Therefore, the angle of attack
  is exactly what you say: the angle between relative wind and the
  fuselage -- and not that of the wing (even though it is arguably more
  important).

While this answer to another related question stated:

From A.C. Kermode; Mechanics of Flight, London, Pitman, 8th Edn,
  1972, p.75 (his bold):

"We call the angle between the chord of the aerofoil and the direction of the airflow the angle of attack.
"This angle is often known as the angle of incidence; the term was avoided in early editions of this book because it was apt to be
    confused with the riggers' angle of incidence, i.e. the angle between
    the chord of the aerofoil and some fixed datum line in the aeroplane.
    Now that aircraft are no longer "rigged" (in the old sense) there is
    no objection to the term angle of incidence; but by the same token
    there is no objection either to angle of attack, many pilots and
    others have become accustomed to it; it is almost universally used in
    America, and so we shall continue to use it in this edition."

And from L.J. Clancy; Aerodynamics, London, Pitman, 1975, p.56:

"The attitude of the aerofoil, as expressed by the angle between the chord line and the free stream velocity vector ... , denoted by
    $\alpha$, is called the incidence, or angle of attack."

In contrast to Kermode, Clancy goes on to use "incidence" throughout.

The current question: while there's no question that "angle-of-attack" is often used to describe the angle between a wing chord line and the flight path/ relative wind, when we are talking about a whole aircraft, "angle-of-attack" is apparently sometimes used to describe the angle between the longitudinal axis of the aircraft and the flight path/ relative wind.
Regardless of whether or not all the statements above are entirely correct, I would like to know--
In one of the two possible British usages of "angle-of-incidence", specifically when it is NOT being used to indicate the "rigger's angle of incidence" between the mean chord line and the longitudinal axis of the fuselage, in the whole-airplane context, is there a default presumption that it means the angle between the longitudinal axis of the fuselage and the flight path/ relative wind, or is there a default presumption that it means the angle between the wing chord line and the flight path/ relative wind, or is there no default presumption as to which of these two alternatives is intended?
By "default presumption" I mean the most common usage or the usage which is least in need of extra clarification to the reader as to what is intended.
The question is not intended to get into the distinction of measuring relative to the free-stream airflow/ flight path/ relative wind versus the local airflow-- that's another thing that may depend on context-- just the distinction of measuring from the wing rather than from the fuselage.
As an aside, I have been informed that that the French phrases for these terms are used in different ways, with "angle d'attaque" referencing the angle between the flight path/ relative wind and the fuselage, and "angle d'incidence" referencing the angle between the flight path/ relative wind and the wing.  But, we can explore the veracity of that idea in some other question.
Clarification -- it seems likely that the usage of "angle of incidence" I'm referencing in this question is now confined to aerodynamics/ design textbooks, papers, etc, and not in widespread usage in the pilot community in Britain.  It's not something you'll find in a current study guide for a private pilot ground  school or written exam, as the American terminology has now become universal there, using "angle of incidence" to mean the angle between the mean chord line of the wing and the longitudinal axis of the fuselage.  That's not the usage of the term that this question is asking about.

Note that this is not a duplicate of https://aviation.stackexchange.com/questions/76682/how-common-is-it-in-current-british-usage-for-the-angle-between-the-chord-line-o because the earlier question was asking how often the term was used to mean the rigger's angle of incidence versus something very different, while this question is asking whether when used in relation to an angle measured from the flight path, the measurement is usually presumed to be referenced to the fuselage or the wing.

Since the wing is most affected by the angle of attack and most sensitive to changes of it, the default angle of attack should be between wing chord and airflow, not some arbitrarily selected reference on the fuselage. Mr. Kermode is right. Just because an answer has been accepted does not mean it is right.

@PeterKampf thank you for your comment, feel free to comment further here if you wish but your point is clearly made.  https://chat.stackexchange.com/rooms/106037/a-room-to-talk-about-american-british-and-french-usage-of-angle-of-attack-a

@PeterKampf you might choose to incorporate the idea that by default "angle of attack" is normally indexed to the wing not the fuselage, at least in some contexts (pilot-speak?  engineering text books? etc) into an answer of your own to the question https://aviation.stackexchange.com/questions/76683/is-there-a-standard-word-or-phrase-in-the-english-speaking-world-to-describe-the/76709#76709 , possibly noting that "angle-of-attack of the fuselage" might be a term for what the question is asking about.

You should edit the title so that it is not needed to open your question to understand what your are asking for. There are many subjects possible for angle of incidence.

@ManuH-- given that titles are limited in length, any suggestions for how to do that?

I don't like this question very much any more; I think it was overly influenced by an incorrect impression of how "angle of attack" was usually used, due to some other recent discussion.

I found your exact question a little confusing, so let me answer with a quote from a current British PPL exam preparation book:

The wing's angle of incidence - the angle between the wing chord-line and fuselage - is fixed by the construction of the wing and the angle at which it is bolted onto the fuselage

Source: AFE Book 4 - Aircraft General Knowledge
I have to say, as a British PPL I would always assume "angle of attack" to mean relative to wind by default and would use angle of incidence to describe the physical design of the aircraft, but would likely understand from context. I.e., saying "The angle of attack on a Piper Warrior is x degrees" would make sense and be understood.
And, to be clear, we would NEVER use angle of incidence to describe the angle to relative airflow.

Some parts of your answer do conflict with some answers in the other questions/ answers linked in my question.  Maybe the usage I'm referencing is now confined to aerodynamics/ design textbooks, papers, etc, and not in widespread usage in the pilot community in Britain.  I'd like to ask you if you would assume "angle-of-attack" to mean, in the whole-airplane context (a pilot is flying an actual airplane). the angle between the flight path/ airflow and the WING, or the the angle between the flight path/ airflow and the FUSELAGE, or no particular assumption either way.

If this gets too involved we'll have to move it to chat-- here's a room I set up just for this sort of topic a few days ago-- https://chat.stackexchange.com/rooms/106037/a-room-to-talk-about-american-british-and-french-usage-of-angle-of-attack-a -- but you could probably get away with a brief reply as a comment here.

PS -- the question has been edited to clarify.  Normally I would worry about the edit invalidating an existing answer, but in this case the edit just reinforced the content that was already in the question without changing the question, and the existing answer was not completely on target with what was being asked in the question.  Nonetheless your answer does shed light on the way these terms are most  commonly used in the pilot community, so that's of value, even if not exactly on target with the question being asked.

@quietflyer Ref your first question - I've never heard or been taught of the idea that the angle of attack is anything other than the wing vs the airflow. Obviously the only way we can alter that in flight is through pitching the whole aircraft so a lot of the time the distinction is immaterial but it's taught as all about the wing

This answer would serve well as an answer (or could easily be adapted into an answer) to the related question https://aviation.stackexchange.com/questions/76682/how-common-is-it-in-current-british-usage-for-the-angle-between-the-chord-line-o/76688#76688 .

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text:
Does joystick position control bank angle in some Airbus aircraft? And what happens when the pilot deflects the joystick when wheels are on ground?
Does joystick position control bank angle rather than directly controlling aileron/spoileron deflection in some Airbus aircraft?
Also, what happens when the pilot deflects the joystick when the all wheels are on the ground and the bank angle (or roll rate) cannot change substantially?
Also, if the pilot is landing and the left main undercarriage assemblies are not extended for some reason, when the wheels on the right main undercarriage assemblies touch the ground, will maintaining a strong right control input on the joystick help delay the left wingtip (or engine nacelle) from contacting the runway, or not?

On all FBW Airbus, the sidestick lateral position normally controls roll rate, not aileron deflection. Only in ground mode of Normal Law, ALT2 and Direct Law does the lateral position control aileron deflection directly. AFAIK there is no mode where sidestick position controls bank angle. Wikipedia article on Airbus control laws.

What makes you think joystick position controls bank angle? It would be useful if you could provide an example or source for that claim

@J.Hougaard - thanks, have edited, not in a way affecting any existing answer.

Great answers, sorry that there is no +2 or +10 option.

Does joystick position control bank angle rather than directly controlling aileron/spoileron deflection in some Airbus aircraft?

To complement @Bianfable's answer, in Normal Law Flight Mode, Airbus FBW families (including A220) command roll rate via lateral stick position up to the artificial spiral stability limit of 33 deg bank (for A220 it's 30 deg). Below 33 deg bank, the aircraft exhibits neutral spiral stability; beyond 33 deg bank, it exhibits positive spiral stability, and lateral stick position commands a steady-state bank angle up to the roll limit of 66 deg (for A220 it's 80 deg).

Also, what happens when the pilot deflects the joystick when the all wheels are on the ground and the bank angle (or roll rate) cannot change substantially?

Upon landing, the Normal Law transitions to Ground Mode, whereby the stick inputs command direct control surface movements. For A320, the lateral control transitions from Flight Mode to Ground Mode in 0.5 sec on ground detection is met, as shown below:

Also, if the pilot is landing and the left main undercarriage assemblies are not extended for some reason, when the wheels on the right main undercarriage assemblies touch the ground, will maintaining a strong right control input on the joystick help delay the left wingtip (or engine nacelle) from contacting the runway, or not?

From this German accident report, in the case of an asymmetric gear deployment, ground signal is generated if "both LGCIUs (Landing Gear Control Interface Unit) detect that one landing gear has been lowered and is under load, and the radio altimeter measures the height above ground as less than 50 ft".
Therefore, immediately upon touchdown, you can expect the FBW to partially resist roll motion; but after 0.5 sec, you will have to use lateral stick to hold the aircraft level until the airspeed is too low to do so.

The sidestick (they don't like it when you call it joystick) is not controlling bank angle, but roll rate in flight. On the ground, the control surfaces are deflected proportionally to sidestick movement in order to perform a check of all surfaces before takeoff.
The details may vary, but this is generally true for all full fly-by-wire Airbuses. From the Airbus A320 FCOM:

Normal Law
When the aircraft is on the ground (in "on ground" mode), the sidestick commands the
  aileron and roll spoiler surface deflection. The amount of control surface deflection that
  results from a given amount of sidestick deflection depends upon aircraft speed. The pedals
  control rudder deflection through a direct mechanical linkage.
When the aircraft is in the "in flight" mode, normal law combines control of the ailerons,
  spoilers (except N° 1 spoilers), and rudder (for turn coordination) in the sidestick. While the
  system thereby gives the pilot control of the roll and heading, it also limits the roll rate and
  bank angle, coordinates the turns, and damps the dutch roll.
The roll rate requested by the pilot during flight is proportional to the sidestick deflection,
  with a maximum rate of 15° per second when the sidestick is at the stop.
When the aircraft is in "flare" mode, the lateral control is the same as in "in flight" mode.

(A320 FCOM - Flight Controls - Lateral Control, emphasis mine)
Similar for the A380:

Ground Law
The objective of the lateral ground law is to facilitate aircraft handling on ground.
The lateral ground law is a full authority control law in roll and yaw, with some yaw damping.
However, for small sidestick deflections, the lateral ground law helps the pilot to keep a small bank
  angle (less than 2 °), using only the ailerons. In particular, when the sidestick is at neutral, the law will
  aim to keep the wings level.
When rudder pedal deflection is close to maximum, yaw damping is removed.
The ground law is gradually phased in during 5 s after touchdown.
[...]
Flight Law
Roll Rate Demand
In manual flight, the normal law provides aileron and spoiler control from the sidesticks, to achieve a
  roll rate which is proportional to the sidestick deflection, independent of the aircraft speed.
With a full sidestick deflection, the maximum achievable roll rate is 15 °/s.

(A380 FCOM - Flight Controls - Flight Control System - Normal Law)
Regarding your second question:
Regardless of the exact mode you are in during landing (first "in flight", then "flare" then "on ground"), the pilots always have roll control available which will help keeping the aircraft level without the left gear until the speed is too low to do so.

Joystick, joystick.

@MichaelHall Don't let Airbus see that :p

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text:
In reference to airspace, what does the FAA mean by "within the lateral boundaries of"? Is this construed to also imply a vertical limit?
Several FARs use the phrase "within the lateral boundaries of" (x airspace).  What does the FAA interpret this phrase to mean?  Specifically, what is the vertical extent of the airspace encompassed by this phrase?
The common-sense interpretation of this phrase would appear to include any airspace whose latitude-longitude coordinates fall within the boundaries of said airspace, regardless of altitude, from the earth's surface all the way to outer space, or at least to the upper limit of the airspace which the FAA has any regulatory authority over.
Otherwise, it would seem to serve just as well to dispense with the "within the lateral boundaries" phrase and simply say "within" (x airspace).
Is there any evidence that the FAA interprets "within the lateral boundaries of" differently than the meaning noted above?
The answer to this question affects the interpretations of certain FARs, describing, among other things, airspace where ADS-B-out is required, airspace where 3 miles visibility is required to enter a traffic pattern under Visual Flight Rules with no special VFR clearance, airspace within which aerobatic flight is prohibited, airspace where prior authorization is required to operate unmanned free balloons, and airspace in which an ultralight aircraft may not be flown without prior authorization from ATC.

I believe the upper limit of the FAA's regulatory authority is FL600, not "all the way to outer space"

@abelenky-- noted-- question modified.

Pertains to several answers to this question-- https://aviation.stackexchange.com/questions/74808/is-ads-b-required-for-flight-under-class-b-airspace-but-outside-the-mode-c-veil

@abelenky Class A ends at FL600; above that is class E up to the limits of national airspace, which is currently undefined. Various treaties set it no higher than the Karman Line.

A big part of me is very reluctant to stir the pot, but recent closure of another question has put a burr under my saddle.  I question the phrase “…of the surface area of Class E airspace designated for an airport”.  This would seem to indicate a vertical limit of some sort, NOT a phrase that uses "lateral".  What is the definition of this term?

@MichaelHall --ASE moderators are very strongly discouraging me from using comments for discussion so I will answer in this chat room -- https://chat.stackexchange.com/rooms/142300/discussion-on-question-by-thatguyrj-what-are-lateral-boundaries

The FAA normally interprets the phrase "within the lateral boundaries of" (x airspace) to mean any airspace whose lat-lon coordinates fall within said boundaries, regardless of altitude, from the earth's surface all the way to outer space, or at least to the upper limits of the airspace which the FAA has any regulatory authority over.
Pilots would be wise to follow this common-sense understanding of the meaning of "within the lateral boundaries of".
However, the FAA is not a monolithic entity, nor is it immune to making the occasional blunder.  On a few occasions, some subset of the FAA has adopted a very different understanding of the meaning of "within the lateral boundaries of".
For example, in the text of a spectacularly misguided Final Rule published on page 51966 of the October 5, 1993 edition of the Federal Register, the FAA implied that the phrase "within the lateral boundaries of the surface areas of ... Class E airspace designated for an airport" would not encompass any Class E airspace higher than the floor of the 700' or 1200' AGL "transition area" that invariably overlies a Class-E-to-surface airspace.
To correct this imaginary problem, the FAA changed the wording of FAR 91.157 from the existing wording

91.157 Special VFR weather minimums Except as provided in appendix D, section 3 of this part, the following special weather minimums and
  requirements apply to operations conducted to or from an airport in
  controlled airspace:  (a) Operations may be conducted only under an
  ATC clearance-- (1) Within the lateral boundaries of the surface areas
  of Class B, Class C, Class D, or Class E airspace designated for an
  airport; and ...

To the new wording

91.157  Special VFR weather minimums ( a ) Except as provided in appendix D,
  section 3, of this part, special VFR operations may be conducted under
  the weather minimums and requirements of this section, instead of
  those contained in 91.155, below 10,000' feet MSL within the airspace
  contained by the upward extension of the lateral boundaries of the
  controlled airspace designated to the surface for an airport. (b)
  Special VFR operations may only be conducted--(1) With an ATC
  clearance...

However, the FAA failed to also change the similar wording of FARs 45.22(a)(3)(ii), 91.155(d), 91.303(c), 91.309(a)(4), 93.152, 101.33(a), 103.17, 107.41, 135.205(b), and 137.43(a), thus implying that none of these FARs should be understood to apply to any Class E airspace above 700' AGL in most cases, or above 1200' AGL in the remaining cases.
This blunder has never been officially corrected-- the text published in the October 5, 1993 edition of the Federal Register has never been officially retracted.

Also, I have links to discussion forums where pilots report being given a similar answer-- that the phrase doesn't encompass any airspace above the base of the overlying E5 transition layer at 700' or 1200' AGL-- when they queried FAA officials about the meaning of FAR 103.17.  Obviously not the mainstream interpretation-- otherwise most of the FARs listed above would make no sense at all-- consider especially 107.41--

future edit - last sentence of first paragraph could be changed to end "or above 1200 feet in most  remaining cases."

This answer would be improved by giving specific examples to support the first paragraph; some may be found in letters of interpretation.

This answer could be improved by phrasing third paragraph in a way that uses a word stronger than "implied" or else gives the full text to clearly show that this is clearly what they meant.

This answer would be improved by giving at least one other example, to support the use of the phrase ". On a few occasions".  These answers could be simply cases where FSDO staffers presented such interpretations.

Possible future edit-- change "imaginary" to "perceived"

Future edit-- also add portion clarifying that "within the lateral boundaries of the surface area" only pertains to portions of airspace that actually contact the surface.

Possible future edit-- address the possible argument that if "surface area" is construed to mean just the footprint on the surface rather than an actual chunk of airspace, then it may be difficult to simply dispense with the "within the lateral boundaries" phrase, even the intention is not for the airspace to extend upward indefinitely.  In fact, the FAA clearly does usually construe "surface area" to mean an actual volume of airspace-- support with examples in answer.

Future edit: re: "thus implying that none of these FARs should be understood to apply to any Class E airspace above 700' AGL in most cases, or above 1200' AGL in the remaining cases." -- change to and thus implying that we are free to let unmanned free balloons go floating through the surface footprint of Class-E-to-Surface airspace directly over airports, as long as we stay above 1200' AFL, in nearly all (or all) cases."

Here is the clearest evidence that can be found in the FARs that the FAA considers the airspace described as "within the lateral boundaries" of a given airspace to extend upwards indefinitely, beyond the actual ceiling of that particular airspace -- see chat posts https://chat.stackexchange.com/transcript/message/62964015#62964015 through https://chat.stackexchange.com/transcript/message/62964146#62964146.  The current answer would be improved by adding this content.

Related: https://aviation.stackexchange.com/questions/65930/far-91-215-b3ii-transponders-significance-of-below-the-altitude-of-the

An interesting point is that in some of the rule-making documents leading up to the September 1993 "alphabet" airspace re-designation, the FAA proposed allowing ultralights to operate in (or within the lateral boundaries of) the surface-level Class E airspace designated for airports so long as these operations were conducted above a certain altitude which I recall was something like 4000 or 5000' AGL-- which was also the standard ceiling that was being proposed at the time for Class D airspace-- the question or answer might benefit from a more thorough note on this fact.

The above comments are intended as suggestions as to how this answer could be edited for improvement; not yet ready to actually post an edited version--


text:
What is an airliner's "green dot speed", and how does it vary with weight, and why?
A related question told us, quoting from an Airbus performance manual,

Green dot speed (minimum gradient) is a function of weight.

Comments under the question stated that the "green dot speed" increased as weight increased.
So-- what is "green dot" speed?  Does it reference some fixed, optimal angle-of-attack?  Perhaps the one that gives the best L/D ratio (glide ratio)?  If so, it would obviously increase with weight, generally being proportional to the square root of the wing loading.  If this interpretation of how green dot speed varies with weight is not the correct one, then what is?

"If this is the case, what is the meaning of the phrase "the rate and gradient of descent magnitudes are reduced at higher weights"?"-- this part of the question is now answered here https://aviation.stackexchange.com/questions/75181/why-does-an-airliner-have-a-shallow-descent-when-heavier-opposite-to-gliders-wi/75217#75217 .  Perhaps doesn't address the main thrust of the question comprehensively enough to justify posting this comment as an actual answer.

In fact I think I'll just delete that part of the question as this would not affect the validity of the existing answer anyway.

"(from green dot to VMO), the rate and gradient of descent magnitudes are reduced at higher weight" Well of course: when heavier the descent rate is reduced. And since you are flying at fixed speed, a lower rate means reduced gradient. This is only valid above g/d and since they assume you never fly above Vmo they range this :from green dot to Vmo :-)

Green Dot (GD) speed is a term used by Airbus. It is named after the symbol on the speed tape. It refers to the speed that results in the best climb gradient in case of an engine failure, but it is close the speed resulting in best L/D ratio with all engines operating.
Airbus defines it as follows:

Definition
GD speed is the engine-out operating speed in clean configuration. In
  other words, it corresponds to the
  speed that allows the highest climb
  gradient with one engine inoperative
  in clean configuration.
  In all cases (all engines operative),
  the GD speed gives an estimate of
  the speed for best lift-to-drag ratio. It
  is also the final take-off speed and it
  represents the operational speed of
  the clean configuration and the recommended speed in holding in clean
  configuration.
  It is represented by a green dot on the
  PFD speed scale and displayed only
  when the slats / flaps control lever is in
  the ‘0’ (CLEAN) position and landing
  gears are not compressed

How is GD determined?
GD speed is computed by the Autoflight systems and is based on the
  aircraft weight. The GD formula has
  been set up so that the resulting airspeed provides the best lift-to-drag
  ratio for a given altitude, air temperature and aircraft weight, in clean configuration with one engine out.
  In some phases of flight, GD is computed to minimize drag and thus, the
  fuel consumption (for example during
  the HOLD phase).

(Airbus Safety First Magazine)
The GD speed is increasing linearly with aircraft weight and slightly increases with altitude above FL200:

(Airbus A320 QRH - 4.01 In Flight Performance - Speeds)
Here is a plot of the GD speed as a function of weight for different altitudes:


text:
What indication has the FAA given that phrases like "surface area of Class E airspace designated for an airport" do or don't include E4 "extensions"?
This question pertains to the airspace of the USA.
The dashed magenta shape on the sectional chart around KGUP depicts the horizontal extent of the Class-E-to-surface at KGUP.  Inside this perimeter, Class E airspace extends all the way down to the surface to protect the instrument approach and departure routes at KGUP by imposing stricter visibility and cloud clearance requirements than would exist in Class G airspace.  In the FAA’s “Airspace Designations and Reporting Points” document (current edition FAA Order JO 7400.11D), this airspace is listed as “E2” airspace.  (See page E-116).  A characteristic of E2 airspace is that it completely surrounds and includes the airport whose approaches it is designated to protect.
The dashed magenta shapes on the sectional chart near KMFR depict the horizontal extent of the Class-E-to-surface “extensions” at KMFR.  Inside this perimeter, Class E airspace extends all the way down to the surface to protect the instrument approach and departure routes at KMFR by imposing stricter visibility and cloud clearance requirements than would exist in Class G airspace.  In the FAA’s “Airspace Designations and Reporting Points” document (current edition FAA Order JO 7400.11D), this airspace is listed as “E4” airspace.  (See page E-186).  A characteristic of E4 airspace is that it does not actually include the airport whose approaches it is designated to protect.
The fundamental reason that E4 "extensions" exist at all, rather than simply being part of the adjoined Class D airspace, is to avoid to imposing a radio communications requirement on VFR pilots passing through this airspace, which may be rather distant from the airport itself, in VMC conditions.  (Note how far the E4 "extensions" extend beyond the Class D circle at KMFR.)  Since E2 and E4 airspace both offer down-to-ground-level protection for instrument approaches, it seems illogical that they should be treated substantially differently by the FARs, apart from the requirement for the establishment of radio communications by VFR conditions in VMC conditions.
Yet many FARs are worded in a way that does seem to leave open the possibility that they are not meant not apply to the E4 "extension" airspace, i.e. that substantially stricter conditions are imposed in E2 airspace than in E4 airspace. (And conversely, in the case of FAR 91.157(a), the possibility seems to be left open that a privilege-- the privilege to operate under "Special VFR"-- may be granted in E2 airspace but not in E4 airspace.)
The crucial issue is whether or not phrases like "within the lateral boundaries of the surface area of Class E airspace designated for an airport", "within the lateral boundaries of controlled airspace designated to the surface for an airport", "within the airspace contained by the upward extension of the lateral boundaries of the controlled airspace designated to the surface for an airport”, and "within a Class E surface area designated for an airport" should be construed to include E4 airspace, i.e. the "extensions" like we see outside the Class D airspace at KMFR.
Here are some of the specific FARs that contain one of these phrases:

A) Certain FARs include the phrase “within Class A, Class B, Class C, or Class D airspace or within the lateral boundaries of the surface area of Class E airspace designated for an airport".  FAR 103.17 uses this phrase to indicated the airspace where prior authorization is required to operate an ultralight aircraft.

B) Certain FARs and other regulations include the phrase “in Class B, Class C, or Class D airspace or within the lateral boundaries of the surface area of Class E airspace designated for an airport“.  FAR 107.41 uses this phrase to indicate airspace where prior authorization is required to operate a “small unmanned aircraft”.    The October 2018 44809 Exception for limited recreational operations of unmanned aircraft ("Recreational Exception") uses this phrase to indicate airspace where prior authorization is required to operate a “small unmanned aircraft”, i.e. a remote-controlled model airplane, hobby "drone", etc, under the terms of the Recreational Exception.

C)   Certain FARs include the phrase “within the lateral boundaries of the surface areas of Class B, Class C, Class D, or Class E airspace designated for an airport”.  FAR 91.155(d) uses this phrase to indicate airspace where 3 miles visibility is required to take off, land, or enter a traffic pattern under Visual Flight Rules with no special VFR clearance.  FAR 91.303(c) uses this phase to indicate airspace where aerobatic flight is prohibited.  FAR 91.309(a)(4) uses this phrase to indicate airspace where a pilot must notify the control tower, or the appropriate the Flight Service Station, before conducting glider towing operations.  FAR 101.33(a) uses this phrase to indicate airspace where prior authorization is required for operation of unmanned free balloons, if those operations are conducted below 2000’ AGL.  FAR 135.205(b) uses this phrase to indicate airspace where a ½-mile daytime, 1-mile nighttime visibility requirement applies to part-135 helicopter operations.

D) Certain FARs include the phrase “within the lateral boundaries of controlled airspace designated to the surface for an airport”.  FAR 91.155(c) uses this phrase to describe the airspace where a Special VFR clearance is required to operate under Visual Flight Rules below a 1000’ AGL ceiling.

E) Certain FARs include the phrase “within the airspace contained by the upward extension of the lateral boundaries of the controlled airspace designated to the surface for an airport”.  FAR 91.157(a) uses this phrase to indicate the airspace where operations under 10,000’ MSL may be conducted under the relaxed cloud clearance and visibility requirements afforded by a special VFR clearance.

F) Certain FARs include the phrase “within the lateral boundaries of the surface areas of Class B, Class C, Class D, or Class E airspace designated for the takeoff airport”.  FAR 45.22(a)(3)(ii) uses this phrase to indicate airspace where prior approval of the responsible Flight Standards Office is required to operate an aircraft bearing non-standard markings for exhibition purposes.

G) Certain FARs include the phrase “within Class B, Class C, or Class D airspace, or within a Class E surface area designated for an airport in which flights are intended”.  FAR 121.347(a)(2) uses this phrase to indicate airspace in which aircraft operating under part 121 under VFR along routes that can be navigated pilotage must be equipped with the radio equipment necessary to communicate with appropriate ATC facilities.

(Note that FAR 137.43(b) has a significantly different construction than the other FARs listed above.  It uses the phrase “within the lateral boundaries of a Class E airspace area that extends upward from the surface” to describe the airspace where a person may not conduct agricultural aircraft operations under weather conditions below VFR minimums without prior authorization.  There seems to be no ambiguity here.  Perhaps there is a specific reason why the other FARs listed above didn’t use the same construction, and included the “designated for an airport” phrase?)

The common thread in all these FARs (except for FAR 137.43(b)) is the phrase “surface area of Class E airspace designated for an airport”, or the phrase “controlled airspace designated to the surface for an airport”, or another similar phrase including the words "designated for an airport" or "designated...for an airport."
The question(s): What (if any) specific indications have the FAA given that this phrasing should be construed to include E4 Class-E-to-surface “extensions” such as those at KMFR?  And what (if any) specific indications have the FAA given that this phrasing should not be construed to include E4 Class-E-to-surface “extensions” such as those at KMFR? And which is the better interpretation of the language of the Federal Aviation Regulations, including the “Airspace Designations and Reporting Points” document, FAA Order 7400.11D?
A couple of additional points may further inform the question:

Here's the primary argument that phrases like "surface area of Class E airspace designated for an airport" should not be construed to include E4 airspace, i.e. the "extensions":

FAR 71.1 establishes that the FAA’s “Airspace Designations and Reporting Points” document, current edition FAA Order JO 7400.11D, is incorporated by reference into the Federal Register, and thus legally constitutes part of the Federal Aviation Regulations, and provides “a listing for Class A, B, C, D, and E airspace areas”.  The Airspace Designations and Reporting Points document (current edition FAA Order JO 7400.11D) uses the following phrases to name or describe E2 airspace: “6002. Class E Airspace Areas Designated as a Surface Area” (page vii), and “6002. Class E Airspace Areas Designated as Surface Areas. The Class E airspace areas listed below are designated as a surface area for an airport.” (page E-1). The same document uses the following, significantly different phrases to name or describe E4 airspace: “6004. Class E Airspace Areas Designated as an Extension to a Class D or Class E Surface Area” (page x), and “6004. Class E Airspace Areas Designated as an Extension to a Class D or Class E Surface Area. The Class E airspace areas listed below consist of airspace extending upward from the surface designated as an extension to a Class D or Class E surface area.” (page E-155).  Should these names and descriptions be considered to be merely supplemental, explanatory content, or do they legally designate E2 airspace as the only subclass of Class E airspace that should be considered to be “designated as a surface area”, and likewise as the only subclass of Class E airspace that should be considered to be "designated for an airport"?  It certainly seems that the authors of the "Airspace Designations and Reporting Points" document went out of their way to avoid applying these phrases to E4 airspace, and to reserve them for E2 airspace.

And here's an argument in support of the idea that phrases like "surface area of Class E airspace designated for an airport" should be construed to include E4 airspace, i.e. the "extensions":

FAR 71.71 lists and describes all Class E airspace.  This is done in large part by reference to the "Airspace Designations and Reporting Points" document (current edition FAA Order JO 7400.11D).   Far 71.71 states: “Class E airspace consists of (a)…, (b) The airspace areas designated for an airport in subpart E of FAA Order 7400.11D (incorporated by reference, see § 71.1) within which all aircraft operators are subject to the operating rules specified in part 91 of this chapter, (c)…, (d)…, (e)…, (f)….”  E4 airspace cannot possibly be described by (a), (c), (d), (e), or (f), because these clauses all describe Class E airspace that does not extend all the way to the surface.  So unless we take the absurd position that E4 airspace is actually not Class E airspace it all, it seems that we are forced to conclude that FAR 71.71 does in fact consider E4 airspace to be “designated for an airport in subpart E of FAA Order 7400.11D”, notwithstanding the titles and descriptions actually used in FAA Order 7400.11D.

What specific guidance has the FAA given on how to resolve the apparent discrepancy between the language of FAR 71.71 and the language of the "Airspace Designations and Reporting Points" document, FAA Order 7400.11D?  In the eyes of the FAA, do phrases like "surface area of Class E airspace designated for an airport" apply to the E4 "extensions", or not?
Please note that this question is only intended to be about the horizontal extent of the airspace that should be considered to encompassed by the meaning of “within the “surface area of Class E airspace designated for an airport”, and other similar phrases — not the vertical extent of this airspace.
Related ASE questions--
Does FAR 91.155c apply to class E surface extensions?
Does an SVFR clearance extend to Echo surface extensions?
Which parts of class E airspace can an ultralight (part 103) fly in without prior ATC authorization?

Similar questions have been asked before but never in a way that tied together all of the different FARs affected by this question.

just an observation and friendly opinion - you obviously have a great deal of knowledge and interest in the subtleties of the various sub-categories of class E airspace, (which I didn't even know existed before you pointed them out in your earlier questions!) but this is in danger of being labeled TLDR.  (too long, didn't read)  I get that this is probably more important for ultralight pilots and I hope you get the answers you are seeking, but I am struggling to find the relevancy.  There is a lot of information in your question to sift through, and frankly I gave up trying...

Make it relevant then.  I have been flying for 37 years and never once have I wondered whether I was in E2 or E4 airspace, or considered what I might need to do differently as a result.

SVFR might be relevant

Not to me it isn't.  If I need to I will go IFR.

@MichaelHall -- How is it useful to say essentially "I would never care about SVFR because I would always go IFR in such cases."?

Re "Make it relevant then. I have been flying for 37 years and never once have I wondered whether I was in E2 or E4 airspace, or considered what I might need to do differently as a result." -- see especially parts C, D, and E of the question.

Part G should read "...along routes that can be navigated using pilotage..."

have you ever heard the term "30 second elevator speech"?  Or executive summary?

FAR 65.37 (f) (2) needs to be added to the list above

Then add it to the list above.

Thanks for the suggestion Michael.  It's amazing how you always are so tuned in to my comments.  You must have some settings selected that I was not aware were possible options.  Anyway, I have been advised by ASE moderators (or whatever you call them) at some point within the last year or two  or three that I should rein in my editing.
There is more work in progress on this particular post, and that is why I will not add the changes to the list above at the present time, but instead will save them till the other changes are ready to go, to reduce the total number of edits.

No special settings, I’m just observant and have noticed that you are the only one who does this.

Plan for future editing-- remove the "what is the best interpretation" part of the question.  Make it clear only asking about FAA issuances after the September 16 1993 airspace re-designation.  Link to a separate question https://aviation.stackexchange.com/q/91120/34686 to address the FAAs original intent during the rule-making process leading up to the September 16 1993 "alphabet" airspace re-designation --

W/a "surface area" alone?

Here are some indications that the FAA has given that phrases like "surface area of Class E airspace designated for an airport" do include E4 Class-E-to-surface "extensions":

In the current Aeronautical Information (AIM), section 3-2-6(e)(2) contains the following sentence (italics and bolding added):

Surface area arrival extensions become part of the surface area
and are in effect during the same times as the surface area.

The above sentence first appeared in the AIM in the 2016 edition, and appears to reflect no specific change in the relevant FARs or the "Airspace Designations and Reporting Point" document.

In relation to item "E" in the present question, and also in relation to FAR 91.157(a) -- consider a case where E4 airspace adjoins Class D airspace with a part-time tower, and the Class D airspace (but not the E4 airspace) is specified in the Airspace Designations and Reporting Points document (FAA Order JO 7400.11D) to convert to E2 airspace during the hours that the tower is closed. (This is quite common, but see this ASE question for an alternative arrangement.)  When queried by telephone about such a case, many Air Traffic Control Center personnel said during the hours the tower was closed and the E2 airspace was controlled by the Air Traffic Control Center, they would have no problem issuing a Special VFR Clearance throughout the entire “Echo Surface Area”, by which they meant all the Class-E-to-surface airspace including the E4 “extensions”.  (However, some other Air Traffic Control personnel said that E4 “extensions” would generally not be included in a Special VFR Clearance in such a case, but due to operational considerations rather than a lack of regulatory authority to include them.  For more details, see this related ASE question.)

And here are some indications that the FAA has given that phrases like "surface area of Class E airspace designated for an airport" do not include E4 Class-E-to-surface "extensions":

In relation to item "E" in the present question, and FAR 91.157(a) -- a related ASE answer provided a (circa) 2010 response from the FAA ATO Western Service Center addressing the question of whether "Special VFR" operations may be conducted in E4 Class-E-to-surface "extensions".  Although the specific example in question was complicated by the fact that the airport's Class D airspace was specified to revert to Class G airspace rather than to E2 Class-E-to-surface airspace when the tower closed for the night, and thus the local ATC Center was not to used to routinely handling requests for Special VFR Clearances for any of the airspace associated with that airport, the FAA ATO Western Service Center's response nonetheless did contain the following passage:

Our opinion is that E4 airspace is not part of the airspace designated
as the surface area for an airport. The surface area for an airport is
D, C, or E2. Extensions are treated differently from surface areas
designated for an airport, ie there is no communication requirement.
In addition extensions, by definition in 7400.9, are not airspace
designated as the "surface area for an airport".

As noted in item "B" in the present question, FAR 107.41 states “No person may operate a small unmanned aircraft in Class B, Class C, or Class D airspace or within the lateral boundaries of the surface area of Class E airspace designated for an airport unless that person has prior authorization from Air Traffic Control (ATC)”.  A memorandum issued on January 8, 2018 by FAA staffer Scott J. Gardner, Acting Manager, Emerging Technologies, AJV-115, stated that according to the FAA's Airspace Designations and Reporting Points document, "The only type of Class E airspace that matches the language in 107.41" is E2 airspace.  The memorandum stated:

In reviewing Class E Surface Area authorization requirements, we
determined that the Class E authorization requirement only pertains to
Class E surface areas for an airport, not the Class E extensions to
Class D, C and E airspaces.

In keeping with item (2) immediately above, the FAA's LAANC system for authorizing flight of Small Unmanned Aircraft under FAR 107 (and also under the October 2018 44809 Recreational Exception for limited (hobby) recreational operations of unmanned aircraft, which uses the same phrasing as FAR 107.41)) does not include any E4 Class-E-to-surface "extension" airspace in the "gridded" airspace where authorization may be requested, thus implying that no authorization is required to operate a Small Unmanned Aircraft System (sUAS) or hobby model airplane, drone, etc in this airspace under the terms of FAR 107 or the October 2018 Recreational Exception.

In keeping with items (2) and (3) immediately above, this 2019 Power Point document entitled "Class E airspace", compiled by FAA Aviation Safety Inspector Kevin Morris for an FAA UAS (Unmanned Aircraft System) Symposium, contains graphics clearly indicating that no authorization is needed to operate an "unmanned aircraft" in E4 airspace-- i.e. in the "extensions" to Class D or E2 airspace-- despite the language of FAR 107.41.  Note specifically the inclusion of KTVL (Lake Tahoe airport) as one of the illustrated examples.

If there were no operational difference between E2 airspace surrounding an airport and E4 "extensions", it is difficult to imagine why the FAA would ever designate an E4 "extension" to full-time E2 airspace, as has been done at Lake Tahoe Airport (KTVL) and Humboldt Country Airport (KACV), rather than simply making the entire area one unified piece of E2 airspace.

The present question goes on to ask:

And which is the better interpretation of the language of the
Federal Aviation Regulations, including the “Airspace Designations and
Reporting Points” document, FAA Order 7400.11D?

It seems clear that the argument "2" in the present question, based on FAR 71.71 and supporting the idea that phrases like "surface area of Class E airspace designated for an airport" do include E4 Class-E-to-surface "extensions", is stronger than argument "1" in the present question, based on the "Airspace Designations and Reporting Points" document (FAA Order 7400.11D) and supporting the opposite view.  Of course, even if the only practical effect of an E4 "extension" were to impose, all the way to ground level, stronger cloud clearance and visibility requirements than the standard Class G requirements, this would still provide some added protection to IFR approach and departure paths.  But it's difficult to imagine that the FAA ever intended that regulations such as FAR 101.33(a), which requires prior authorization for the operation of unmanned free balloons below 2000' AGL, should not apply in the E4 "extensions" that protect the approach and departure paths.
Before the 1993 airspace re-organization that gave us the current "alphabet" classes, all of the FARs listed in the present question (except those not yet in existence) simply referred to "control zones" rather than using phrases like "surface area of Class E airspace designated for an airport".  Since at that time, communications requirements were not contingent upon whether or not a given airspace was within a "control zone", there was no need for the control zones to have "extensions".  The "control zones" were simply sized and shaped as needed to include all the airspace where it was desired that enhanced cloud clearance and visibility requirements be extended all the way to ground level.  The FARs were written such that the same boundaries were also used in relation to SVFR authorization, the prohibition of aerobatics, the requirement for special authorization for ultralight flight or unmanned free balloon flight, etc, as per the various FARs listed in the present question.  However, at the time of the 1993 "alphabet" airspace re-organization, the regulations had to be converted into new phraseology, since "control zones" no longer existed.  Arguably, at this point in time there was a failure to adopt clear and consistent language that would have allowed the newly modified versions of the FARs to mesh easily with the new "Airspace Designations and Reporting Points" document, and ever since then, confusion has existed within the FAA as well as within the pilot community as to whether or not the dozen or so FARs listed in the present question do or do not apply to E4 "extensions".  (Read more about this history in this related ASE answer.)
Here is one of the more astounding results of the ongoing confusion and ambiguity around this issue.  It seems obvious that when the October 2018 44809 Exception for limited recreational operations of unmanned aircraft ("Recreational Exception") was created-- undoubtedly with substantial FAA input-- the authors assumed that by including the phrase "within the lateral boundaries of the surface area of Class E airspace designated for an airport" within the list of places where prior authorization was required, E4 airspace would become off-limits for recreational model aircraft, or accessible only under strict conditions, including an altitude limit prescribed at the time the authorization was issued.  The legislation contains no other provision for limiting the altitude to which model airplanes, hobbyist drones, etc may be flown in E4 airspace.  Therefore the FAA's assertion that E4 airspace does not fall within the meaning of  "within the lateral boundaries of the surface area of Class E airspace designated for an airport" has the bizarre consequence of setting aside E4 airspace-- the airspace protecting instrument approach and departure paths-- as the only airspace in which model airplanes, hobbyist drones, etc may be flown with no altitude restriction whatsoever.1  This is not the case for part 107 operations, because part 107 contains a blanket 400' height limit, with certain well-prescribed exceptions.
Footnotes--

Actually, the plot is even more twisted than that-- the case may be made that after using the E4 airspace as an "elevator shaft" to ascend from ground level to the floor of the overlying sheet of Class E airspace (typically at 700' AGL or 1200' AGL), a model airplane or hobbyist drone pilot operating under the Recreational Exception may then freely roam around the Class E airspace at any altitude above the Class E floor, without being confined to stay within the footprint of the E4 extension.  The key point being that unlike the situation with Part 107, the 400' altitude limit in the Recreational Exception only applies in uncontrolled airspace.

This answer would benefit from the inclusion of content related to the following: regarding the issue of the apparent lack of any altitude limit, as well as any apparent requirement for "prior authorization", for rc hobbyists' model airplanes, "drones", etc in E4 airspace (the "extensions") -- one FAA staffer attempted to resolve this issue by way of the following response -- https://www.rcgroups.com/forums/showpost.php?p=43098213&postcount=11 . (ctd...)

(ctd) Note that the staffer does not argue that any prior authorization is required for operations under 14 CFR 44809 in E4 airspace. In fact, the staffer specifically writes "or surface E airspace designated for an airport (E2)", essentially acknowledging that "surface E airspace 'designated for an airport'" can be reasonably construed not to include E4 airspace, which means that no prior authorization is required for hobbyist model airplane/ drone/ etc operations in E4 airspace under either 14 CFR 4480 (the "Recreational Exception") or Part 107 . (ctd...) –

(ctd) The rest of the staffer's response is basically non-logical-- in essence he seems to be saying "we forgot to adequately spell out what restrictions we'll impose on you if you engage in this particular activity (flight in E4 airspace) which would otherwise be allowed under 14 CFR 44809 (the "Recreational Exception"), and this oversight leads to bizarre results, so therefore you are not permitted to engage in this particular activity under 14 CFR 44809, so you are controlled by Part 107 whenever you are in E4 airspace.  And Part 107 imposes a blanket 400' altitude ceiling, apart from (ctd)

(ctd) And Part 107 imposes a blanket 400' altitude ceiling, apart from some specific exceptions."  That simply doesn't compute.  Just because the FAA failed to set an altitude limit for hobbyist model airplane / drone flight in a certain airspace (E4 airspace) under the terms of the "Recreational Exception", doesn't logically imply that flight in that airspace may not be conducted under the "Recreational Exception".  Only if one takes it as a "given" that the regulations contain no oversights and never produce illogical results, could that sort of argument "hold water".

This answer would benefit from the inclusion of content relating to the following-- there are instances where the FAA uses the phrase "Surface Area", even without the additional phrase "... designated for an airport", to signal that E2 airspace is being referenced and E4 airspace is not being referenced.  Examples: NPRM on airspace expansion...

The E4 extension at KTVL has now been removed.  However, SIT/PASI is now a new example of an airport with a core E2 circle and a very large E4 extension.  Note that the FAA seems to have now standardized on the practice of not showing the boundary between E2 and E4 airspace on the sectional charts.  This answer needs to be updated to reflect these points.

Re the first item in this answer-- the content in the AIM-- similar content appears in the Chart Supplement (Formerly Airport/ Facility Directory) and has at least since May 2007 and possibly much sooner-- as noted on page 6, "Meeting 07-01", here https://www.faa.gov/air_traffic/flight_info/aeronav/acf/media/RDs/07-01-195_Depiction_of_Class_E_Surface_Areas.pdf -- full May 2007 meeting minutes here https://www.faa.gov/air_traffic/flight_info/aeronav/acf/media/minutes/ACF_07-01_Minutes.pdf

See also comment at "Meeting 07-02" (October 24-25 2007) on page 6 here https://www.faa.gov/air_traffic/flight_info/aeronav/acf/media/RDs/07-01-195_Depiction_of_Class_E_Surface_Areas.pdf -- MEETING 07-02: Mr. John Moore, NACO, recapped this issue.... For some time (since the Airspace Redesign) it has been assumed that “Arrival extensions for instrument approach procedures become part of the primary core surface area." -- Full minutes of "Meeting 07-02" here-- https://www.faa.gov/air_traffic/flight_info/aeronav/acf/media/minutes/ACF_07-02_Minutes.pdf --

This content will be integrated into this answer in the near future--

Also highly relevant -- https://aviation.stackexchange.com/a/92260/34686 -- pertains to the first item 1 in the list.  The content was in the A/FD (now Chart Supplement) long before it was ever in the AIM.

Item 5 ought to be deleted-- doesn't really constitute very strong evidence of anything-- especially in light of https://aviation.stackexchange.com/a/55806/34686 .

The "does not include E4" section of this answer needs to be updated to include the memo reproduced in this answer -- https://aviation.stackexchange.com/a/55806/34686

Here's a 2000 legal interpretation that appears to support the "does include E4" position -- https://www.faa.gov/sites/faa.gov/files/faa_migrate/interps/2000/reeves_2000_Legal_Interpretation.pdf . To confirm an E4 "extension" is involved,  I need to obtain a copy of a sectional showing the airspace as it appeared at this time, since the earliest vesion of the FAA's "Airspace Designations and Reporting Points" document that is available on line appears to be JO 7400.9N, https://www.faa.gov/regulations_policies/orders_notices/index.cfm/go/document.information/documentID/14941, issued 9-1-2005.


text:
In the US, are there any operational control towers located in surface-level Class E airspace or in Class G airspace?
(This question pertains to the airspace of the United States.)
FAR 91.126 gives some general rules for operating at or near airports in Class G airspace, and FAR 91.127 gives some general rules for operating at or near airports in Class E airspace.
Section (d) of 91.126 and section (c) of 91.127 pertain specifically to operations at airports with operational control towers.
a) This seems to beg the question, are there any operational control towers located in surface-level Class E airspace or in Class G airspace?
b) Were there ever?  (Counting from the September 16, 1993 "alphabet" airspace re-organization onward.)
c) If "no" to a and b, then what is a practical example of how a pilot's behavior might be altered by the need to comply with 91.126(d) or 91.127(c)?  After all, it appears that generally speaking, it is not possible to get within 4 nautical miles of an airport with an operational control tower, at 2500' AGL or below, without entering Class D (or higher) airspace.

This answer indicates that LCQ, a towered airport, used to be in Class G airspace.

@randomhead -- good find-- and I see that the airspace has now become Class D there.

A 2016 comment under this answer https://aviation.stackexchange.com/a/29824/34686 references KTME as another example of a towered airport in Class G airspace; it too is Class D now.

Back to LCQ, this question makes it sound like the tower was perhaps newly installed and the chart hadn't been updated—it was actually Class D when the tower was operational. Perhaps.

And my discussion with Dean F. under this answer led me to a document describing a temporary ATCT, which would turn the airspace from Class G to Class E.

@randomhead -- I wonder why they didn't just go ahead and make it temporary Class D --more complex to accomplish?

@randomhead -- re document cited in your last comment-- I'm not sure whether they really did make it surface-level Class E-- see my comments under TrevorJohn answer--

@randomhead -- I see room for a new ASE question here, asking if they really did make the airspace at DeLand be temporary surface-level Class E, or not.  But, enough for today-- maybe someone else will wish to ask it--

@randomhead-- have now deleted those comments, but basically, they just explained that I confirmed the airspace at DeLand was normally class G (up to 700') back in 2016, and I did a NOTAM search that turned up a reference to the temporary control tower but no reference to a change in airspace status.

Nearly ten days after this string of questions was started, it finally occurs to me to ask, if the airport is in Class G airspace (i.e. that's what the airspace is at ground level), but the aircraft is in overlying Class E airspace, at that instant in time, which rules govern the aircraft, 91.126 or 91.127?  In other words, does the word "in" in the title of the regulations refer to the word "airport", or to the word "operating"?

I read it the former way, hence my conclusion that the existence 91.127c kind of implies that the FAA envisioned that there were, or might be, towered airports in surface-level Class E airspace. But I can see that it is not completely unambiguous, and some of the answers might have been written from the viewpoint that the purpose of 91.127 might be to govern aircraft coming in to land at an airport located in (surface-level) Class G airspace, while those aircraft are still in the overlying Class E airspace.

There are a handful of towers still in surface Class E/G airspace. They're rare, but they do exist and are something to watch out for during preflight planning.
As of April 2021, here's the airports I know of:

KJYO - Leesburg, VA
KPCA - Picacho ARNG, AZ
KTNX - Tonopah Test Range, NV (inside restricted airspace)

I wouldn't be surprised if there's others I missed, these aren't really cataloged anywhere.
Many of these do eventually become proper Class D airports once they have proper weather reporting capability. For example, KTRK (Truckee, CA) was an infamous one on the west coast that just got its Class D ring in 2017.
You'll also see temporary towers pop up via NOTAM for special events. These NOTAMs don't change the airspace designation, since changes to airspace need to go through the formal rulemaking process.

Since the question references surface-level Class E airspace, you might want to clarify that first sentence refers to "Class G airspace at the surface  (with Class E airspace above)"-- if that's what you meant.  On the other hand, maybe you did mean Class G airspace or surface-level Class E airspace, though no examples were provided of the latter.

At areas where a local increase in traffic density occurs, a temporary tower may be installed.  This may be at an uncontrolled airport which may be in class E, or even Class G airspace. By definition, whereas class G is uncontrolled airspace, adding a control tower does require a Notice to Airmen alerting to the change in airspace and the requirement of the control tower at that location.  This information will be cited by NOTAM and announced on ATIS and airport advisories.
Temporary towers are typically erected at airshow events, or places where a sudden local increase in traffic has occurred, such as during firefighting operations.
Controllers will be typically FAA controllers, or sometimes retired controllers on a contract basis, or operating with a contractor, in a mobile airport traffic control tower (MATCT).  They will be monitoring the common traffic advisory frequency for aircraft that arrive without knowing that a tower is in operation, and in most cases, will quickly advise the arriving aircraft of the tower operation.
It's a pilot (legal) responsibility to become familiar with all aspects of the flight, including checking all NOTAMs.  Temporary towers are NOTAM'd prior to going into operation, typically a day or two prior if the advance notice is there, so there's little excuse for blundering into a temporary tower and not knowing its there.
There are towers in Class G airspace, or towers that lack Class D airspace, because the tower or airport lacks the weather reporting capability, which is a requirement for establishing Class D airspace.  As the original poster noted in his question, 14 CFR 91.126 covers Class G airspace, and 91.126(d), in the context of Class G airspace, addresses a requirement to establish communication with a control tower prior to 4 nm from the airport.
https://www.ecfr.gov/cgi-bin/text-idx?SID=b7ed8006f4088b8259a4bd7380008c24&mc=true&node=se14.2.91_1126&rgn=div8

Good answer; phrase "adding a control tower does require a Notice to Airmen alerting to the change in airspace" seems to imply that the airspace may be temporarily designated as Class D (or surface-level Class E?) in the case of a temporary tower; if so you might want to state that more explicitly. I'm not clear as to whether temporary towers are sometimes, usually, always, rarely, or never accompanied by temporary designation of Class D (or surface-level Class E) airspace-- if rarely or never, might be a way to phrase that w/o mentioning a "change in airspace"-- –

Yes, there is a tower in G (with E above), you just can't fly there
Surface-level controlled (alphabet) airspace isn't allowed to overlap special-use (R-area) airspace, as can be noted from the situation at Creech AFB.  This means that the tower (Silverbow Tower) at Tonopah Test Range (KTNX) isn't in controlled airspace as the airport is within the bounds of the Nellis Range Complex.  Of course, that also means that it doesn't see civil traffic, only USAF "black" operations, JANET flights on behalf of the DoD, and the occasional emergency knockoff from normal Nellis Range operations I'm sure.

I'm not sure I agree with your premise. The intro section of the wiki article on US airspace says that "airspace class" (A/B/C/D/E/G) and "airspace category" (unrestricted, restricted, prohibited) are not mutually exclusive. The airspace designers may have chosen to not allow the Creech Class D to enter R-4806W, but the airspace is still controlled (Class E). No?

@randomhead -- you do make a good point in that the presence of SUA doesn't affect the normal E/G split at 1200' AGL, amended the answer to clarify that that isn't affected


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Has this type of "gyrocompass" ever been used in an aircraft?
One type of instrument commonly referred to as a "gyrocompass" is commonly used in ships.  It detects true north based on gyroscopic precession, and is not slaved to any magnetic compass or any magnetic sensor of any kind, nor is it necessary that the instrument be frequently manually corrected by reference to a magnetic compass.  Has this instrument ever been used in aircraft, and if so, what are some examples?
The intent of the question is to ask about specifically about instruments that benefit from an intrinsic north-finding property related to the earth's rotation, including cases where this property is used to correct for various errors that would otherwise eventually cause the system to drift out of its initial orientation.

Since aircraft will regularly go electrically dark for extended periods of time I don't see how this could be a viable option for navigation.  All the gyro based compass systems I have seen are either slaveable to current heading or get magnetic info.

Aircraft use Inertial Navigation Systems (INS) and Gyroscopes are part of the INS.   https://en.wikipedia.org/wiki/Inertial_navigation_system

In hindsight the "steaming error" thing should have been obvious, but the question gathered an interesting answer nonetheless.

@Mike Sowsun: SOME aircraft may use inertial navigation systems, but a great many don't.

Yes, I should have said some aircraft use INS and some INS use Gyroscopes.

@JeffA A gyrocompass (which is distinct from a gyroscopic heading indicator) uses the rotation of the Earth to find true north (not magnetic north). So it will (eventually) align itself when it's switched on, with no need to reference any other navigation instruments.

I think the answer is "no and yes".  Bear with me...  That sort of device as a stand alone heading sensor has never been used in an aircraft and if you parse the Wikipedia article carefully it becomes apparent why, under the paragraph titled "Errors".

A gyrocompass is subject to certain errors. These include steaming error, where rapid changes in course, speed and latitude cause deviation before the gyro can adjust itself.[12] On most modern ships the GPS or other navigational aids feed data to the gyrocompass allowing a small computer to apply a correction. Alternatively a design based on a strapdown architecture (including a triad of fibre optic gyroscopes, ring laser gyroscopes or hemispherical resonator gyroscopes and a triad of accelerometers) will eliminate these errors, as they do not depend upon mechanical parts to determinate rate of rotation.[13]

To work it requires a very slow moving and stable platform (like a ship). Anything approaching rapid motion, even by ship standards, let alone by aircraft standards, requires external help of some kind.
This rules out aircraft, and small boats for that matter I expect.
"Gyrocompass" in aviation has always referred to a directional gyro that is continuously slaved to an external magnetic north sensor.  The traditional system has some form of directional gyro, either right in the instrument panel or built into an Attitude/Heading Reference System (AHRS) unit that drives the cockpit heading indication, with the actual magnetic field sensor in a remote location, usually out at the wing tip, called a Flux Valve, that provides a continuous magnetic north reference, to which the gyro is aligned.
When not slaved to the Flux Valve, an aircraft gyrocompass becomes just a directional gyro, which must be set manually and corrected for precession manually (on an AHRS system you will have a MAG/DG switch that allows you to select slaved or unslaved indications - in the high arctic where compass indications are useless, you have to operate in DG mode).
Now, I said "stand alone" for a reason. Inertial Reference Systems (or Inertial Navigation) used for aircraft navigation do use this phenomenon for their initialization alignment process.  IRS initialization/alignment is done normally on the ground with the aircraft stationary, but can also be done in flight if heading is held steady during the alignment. The system is told where the aircraft is geographically, by entering lat/long or by GPS/FMS input if equipped, and the IRS senses precession from the earth's rotation to figure out what direction the airplane is pointed relative to true north (because it can sense the west-east axis of the earth's movement and knows the airplane longitudinal axis relative to that).  This is how IRS systems get their directional starting point, from which future indications are derived from inertial changes from the starting point.  If inertial errors build up in the system (you get left right IRS position comparator errors), the system has to be aligned again (which is why there is usually a procedure to do an "IRS Align" in flight where you fly a constant heading, speed and altitude for several minutes while the IRS does its thing).
So the answer is, yes, but limited to IRS systems when starting up, and no as a stand-alone heading device.

Please tell me the Flux Valve feeds into a Flux Capacitor on its way to the AHRS! That would just make my day complete!

Phhhhhht.. that gag is, like, so 80s lol.

@JohnK Don't you mean "Will be so 80s"?

@HiddenWindshield  Just clicked that that's another Back To The Future gag.  Clever!

The modern equivalent is the ring laser gyro, a gyrocompass made out of light. A laser beam is split, with each half being bounced round the same triangular cavity but in opposite directions. The interference patterns between the beams are very sensitive to rotation.
Laser gyros are cheaper and all-round better than mechanical gyros. Most modern inertial navigation systems (INS), be they land sea or air, are nowadays based on them. One unit is typically adequate for land and sea, but three are needed for an aircraft; one for each axis of rotation in pitch, yaw and roll.


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What causes a jet airliner (with a yaw damper) to roll toward the "weaker" engine during an asymmetrical thrust condition?
Please help me better understand what causes a jet airliner (such as the Boeing 737-500) to roll toward the "weaker" engine when power is reduced on one side.
Such as in the situations featured in 6:36 through 7:54 and 21:50 through 23:20 in this "Mentour Pilot" YouTube video about the January 9, 2021 crash of Sriwijaya flight 182.  (Links to set to start at segments: 1, 2.)
My specific questions center around how the yaw damper affects the situation, compared to what we'd see in a twin-engine airplane with no yaw damper.
Is the situation simply that the asymmetrical thrust creates a yaw torque that directly leads to the aircraft flying in a slipping condition, as would be measured by a yaw string at the nose?  Which then creates a roll torque via aerodynamic coupling between slip and roll, due to sweep and dihedral?  Is this the dominant source of the roll torque toward the weaker engine?
How is the yaw damper responding to the asymmetrical thrust condition?  Is it attempting to maintain a zero-sideslip condition, as would be measured by a yaw string? Or as would be measured by a slip-skid ball (inclinometer)? But is unable to do so?  Why is it unable to do so?
Or is it likely that the sideforce from the deflected rudder, acting high above the CG of the aircraft, is in fact the dominant source of the roll torque toward the weaker engine?  (It seems that this is what we might expect if the yaw damper was in fact able to maintain a zero-sideslip condition, as measured either by a yaw string, or by the slip-skid ball.)
Or alternatively, could the effect of the jetwash on the airflow near the wing be the dominant source of the roll torque toward the weaker engine?

Related: https://aviation.stackexchange.com/questions/6391/what-is-the-yaw-damper -- note that the answers do not seem to agree about exactly what the inputs to the yaw damper actually are.

What we're really talking about here is skid, not slip.  But from an engineering perspective , as opposed to a pilot's perspective, any condition where the nose is pointing differently than the airplane is actually moving, yaw-wise, is often referred to as slip or sideslip, without intending to specify whether nose is yawed toward "inside" of actual direction of curving flight path (skid), or toward outside (slip-- also applies to linear flight path.)  (There's even an ambiguous area where flight path is curving toward high wingtip-- do you call that a slip, or a skid?!?)

The reason is that yaw dampers normally have only limited authority, maybe 1/4 to 1/3 the available rudder travel, since they are only intended to counteract aileron adverse yaw and dampen any dutch roll tendency.
It's just sensing lateral accelerations and working the rudder to remove them; it doesn't know why. All that happens is the yaw power of asymmetric thrust, beyond a point, will exceed the YD's range and ability to correct.
If you ease back the thrust on one engine while in cruise, the YD will apply rudder to keep the "brick" (skid ball) centered, but it will soon hit its authority limit at some level of thrust differential, and unless you start to apply more rudder with your feet, the airplane will start skidding toward the low thrust engine. With swept wings, any amount of yaw, especially at high speed, you start to get a roll into the yaw immediately.

Got it.  Last two paragraphs of question then become superfluous as those effects are presumably only minor relative to the rest.

Yes. It's like you hired a troll who sits in a closet with a skid ball and rudder pedals, and you tell him just keep the ball centered at all times. On FBW airplanes the YD function is integrated into the multiple FBW computer channels, and I don't recall if its function is still limited the way a mechanical one is. You also often have rudder travel limiter system to limit pilot input at high speed for structural protection. Or, as in the CRJ200, the 3 rudder hydraulic PCUs simply can't push hard enough to get full travel above a speed, and a mechanical travel limiter wasn't necessary.

This is interesting though, including link in first comment below that answer -- https://aviation.stackexchange.com/a/6393/34686 -- (doesn't pertain directly to main thrust of question, which you've answered, but it seems that sometimes yaw rate is an input as well? )

Also of interest -- https://aviation.stackexchange.com/questions/90943/what-is-the-difference-between-the-series-and-parallel-yaw-damper-systems-for-th/90949#90949 -- statement "Because it would oppose any rudder applied to counteract the swing from a failed engine, it was only engaged..." -- why?  I'm figuring what's really being counteracted is the pilots attempt to quickly "swing" the nose back to a condition closer to zero slip, after it's already "swung" into  a slipping condition?  Again because yaw rate is an input?  Not sure, or maybe there is just something wrong with statement--

But that's another question--may have to ask it--

Yaw rate will be a factor in the gain of the YD response, but the main issue is its authority is limited to well below normal rudder travel b/c its job is limited adverse yaw and DR damping. YDs are not intended to do anything about engine failures, and they have almost no effect. If you lose an engine after rotation, if you don't get the rudder in with your foot post haste you might find yourself with the wing tip hitting the ground.

Step back a little. It really is much easier then you are making it out to be.
You know that a rudder induces yaw by introducing asymmetrical drag around the vertical axis, then to damp unintended yaw just means using some counter-rudder. That is all a Yaw damper does. Its sensors detect unintended yaw and operate the rudder (or part of it) to counter the effect. A rudder is not the only way of inducing yaw, anything that adds an asymmetrical force around the vertical axis will induce yaw, which is why without a yaw damper, you have to 'step on the peddle' when rolling a plane. If you have a yaw damper, it will step on the peddle for you. However, there are limits to how much yaw a damper can overcome. Push one engine to max or pull the other to idle and you have a lot of asymmetrical force to counter. As the aircraft yaws in response, the thrust from the dominant engine continues the accelerate the rate of rotation and if it is not addressed early enough, it may induce yaw beyond the ability of the yaw damper or even the rudder to address.

@quietflyer - that is correct. Balanced flight with two engines, and thrust from each is parallel to direction of motion, so yaw forces are balanced. Add yaw and thrust is no longer parallel or balanced which increases yaw further.

@quietflyer - yaw is rotation around the vertical axis. Yaw rate and sideslip are different things again.

Let us continue this discussion in chat.

@quietflyer - Your specific question "How does yawing in and of itself create a thrust asymmetry,..." The application of thrust (or drag) that does not go through the center of lift induces a turning moment. In twin (and quad) engine planes that moment is balanced and parallel to the velocity vector. When the aircraft yaws, the thrust is no longer parallel to the velocity vector so introducing another turning moment.

New content has now been posted to the chat link https://chat.stackexchange.com/rooms/142952/discussion-between-quiet-flyer-and-paul-smith, and  I'd encourage any ASE users wishing to make "discussion"-type comments to this question to join in there.

is it likely that the sideforce from the deflected rudder, acting high above the CG, is in fact the dominant source of the roll towards the weak engine?

It was noticed that the aircraft actually had roll input in the opposite direction of the way in actually was rolling due to thrust asymmetry "skidding" the aircraft.

above cross-over speed, roll control is sufficient to counter-act rolling forces created by a rudder "hard-over", or full rudder deflection.

So, it seems the yaw damper, with its limited travel, is less responsible than the wing sweep and dihedral, and any roll resulting from rudder inputs by design can be counter-acted with the yoke.

"raise the dead"

Slipping away from a dead engine helps counter-act yawing forces from the live one.

could the effect of jet wash ... be the dominant source of roll torque?

This is actually more true of wing mounted propellers.  The live engine prop wash over the wing will cause it to roll into the engine out side.  It would be interesting to compare the rolling effect of a straight wing prop vs a swept wing jet "live" side.

what are the control inputs if one engine completely shuts down?

This would seem to be the path to fully understand what control options competant pilots would have in this situation.

One little observation-- "It was noticed that the a/c actually had roll input in the opposite direction of the way in actually was rolling due to thrust asymmetry "skidding" the aircraft."-- yes, due to the autopilot.  But not full aileron input-- the autopilot was limited to 19 degrees of yoke travel for roll (that is stated at 21:06, just before the start of the second segment mentioned in question.)  So I don't think that simply be virtue of being over "crossover speed", we can be certain that the rudder wasn't responsible.  However, the accepted answer has made a good case for this.

@quietflyer yes, I will edit to "somebody has to fly the plane".  Interesting that coordinated rudder and aileron input into the live engine can be helpful.  The note is a good point.

@quietflyer we need the engine out procedure for the 737-500.  Above "cross-over" speed, a fully deflected rudder can be controlled with aileron input.  In this case, can an engine out asymmetry be controlled with good rudder and aileron.  I would think so.

Cross-over speed relates authority of the ailerons and the rudder.  VMC relates authority of the rudder to oppose a failed engine.  Speed increases control authority, but the speed at which the first two balance isn't necessarily (or typically) the speed at which the latter two balance.  In the Classic 737, your clean crossover speed is around 200 to 210 knots; your VMC would be well below that.

@RalphJ that is excellent info. The 737 engine out procedure number 1 is "maintain directional control".  Perhaps the OP is pointing out that automated systems could have done more to control the engine out.  But this leads to a deeper question, is lack of work load as dangerous as too much.  Especially in the second video, the pilots did not seem to be focused on flying the plane until it was too late.